Rebels from Syria's front lines will be represented in peace talks with the Assad regime for the first time in Switzerland today, despite concerns that the opposition is too remote from events on the ground.

The Syrian Revolutionary Front, a new rebel alliance backed by Saudi Arabia, the United States and the West, has sworn allegiance to the main political opposition grouping, the Syrian National Coalition. The coalition's leader, Ahmed Jarba, will speak at the opening of the conference, appearing in the same room with Walid al-Muallem, the Syrian foreign minister, and other Assad regime representatives.

It will be the first time either side has taken part in peace talks.

The creation of the Syrian Revolutionary Front out of the ashes of the Free Syrian Army, which had been eclipsed by hardline Islamists, represents a diplomatic coup for the US and Saudi Arabia, which were determined to show the side they were backing at the talks was not remote from the people it were supposed to be representing.

"There's absolute FSA backing for a political process that leads to tangible results," a source close to the Front said. "The opposition is pursuing a dual track strategy, to protect the Syrian people against Assad's genocide and to prove to the world that we are a legitimate and credible partner in a political process."

However, all sides have poured cold water on any hopes that the talks, which begin in Montreux with statements of position today and move to Geneva for detailed negotiations on Friday, will lead to any concessions or settlement. President Bashar al-Assad, in an interview, described a proposal for a power-sharing agreement as a "good joke".

Iran, Assad's main sponsor, refused to sign up to that proposal, enshrined in the so-called "Geneva 1 Communique" and will not be present.

Western diplomats say they remain determined that Assad must step down for peace to return to Syria, and suggest the most that can be expected is an agreement for localised ceasefires and the delivery of humanitarian aid.

Assad also offered a ceasefire in Aleppo and a prisoner exchange.

John Kerry, the US secretary of state, and Sergei Lavrov, the Russian foreign minister, were due to meet last night, while President Barack Obama spoke to his Russian opposite number, Vladimir Putin, by telephone. But while the West still hopes that sooner or later Russia will withdraw support from Assad, there is still no indication that this is anywhere near happening.

The West comes to the talks armed with new revelations of the regime's brutality after a report by three international prosecutors, which presented photographs and other evidence of the deaths by torture of 11,000 prisoners in Syrian jails, provided by a regime defector.

"This report is extremely alarming, and the alleged scale of the deaths in detention, if verified, is truly horrifying," said a spokesman for Navi Pillay, United Nations human rights commissioner.

However, the Geneva 1 communique contained no mention of prosecuting regime members for human rights violations, merely referring to "accountability for acts committed", so there is no forum for discussion of such matters at these talks.